Electromagnet



l.. LARSEN.

ELECTROMAGNET.

APPLICATION FILED ocr. 29. 19m.v

. Patented Dc. 6, 1921.

2 SHEETS-SHEET l.

M W INI/mmf? "l" M11-ra Afro/mns L. LARSEN.

ELECTROMAGNET.

APPLICATION FILED OCT. 29. 1918. 1,399,350, Patented Dec. 6, 1921.

2 SHEETS-SHEET 2- FIG .3.

NVENTR ,4 TTOHNEYS UNITED STATES PATENTKOFFICE.

LOUIS LARSRN, or BROOKLYN, NRW YoRK, assis-NOR To snNnH RnnorRro cora- PANY, on New YORK, N. Y., n coRioRATroN or NRW YORK.

nLncTR-oianeNnr.

Specification of Letters Patent.

Patented nee. c, leer.

Original application filed January 2, 1918, Serial No. 299,842. Divided and this application filed October 29, 1918. Serial No.

To all whom it may Concern.'

Re it known that l, Louis LARsnN, a citi` een ot the United States, residing in the city of New York, borough ot Brooklyn, county or" Kings, and State ot New York, have invented a certain new and useful Electromag` net, of which the following is a specification.

My invention relates to an electromagnet of the type which is operative only when the exciting current Vwhich is supplied to its actuating coil falls within certain predetermined limits and whiclubecause of such characteristics, has been `principally employed for the operation of the switches of motor controllers where, their actuating coils being successively connected in series with the motor, the switches will remain open or inoperative so long as the current to the motorie above the predetermined safe value and thus provide a so-called currentlimit system of' control responsive to the electrical condition ot the motor.

As heretofore constructed, the magnets ot these switches have been actuated by a single series wound coil and the magnetic circuit, which includes the usual operative or pulling-in air-gap between one pole ot the fixed magnetic member and one end either of a reciprocating core or of a pivoted armature and a substantially closed magnetic path from the opposite pole oit' the fixed magnetic member back to the movable core or armag ture, is provided with an additional return path or by-pass across an oj posing or holding-Out air-gap maintained between the pole Ot the fixed magnetic member and the end oit the core or an arm of the pivoted arma-y ture opposite that at the pulling-in air-gap. The closed or main branch of the return magnetic circuit in eect short circuits the by-pass across the second or holding-out airgap, and the parts are so proportioned and adjusted that this main path will be saturated with lines ot force lby comparatively small currents while it will require a heavy current to saturate the by-pass. Thus, when excited by a current materially higher than that for which the magnet is constructed and adjusted, enough of the magnetic flux will be forced through the by-pass and across the holding-out air-gap to prevent operation,

but, as the current falls, a larger andglarger -proportion ot the total linx, which is decreasing in all parts ot the magnetic circuit,

conce.

until, the current having fallen within theV limits predetermined, the weakening flux across the pulling-in air-gap will overcome the more rapidly reduced flux across the holding-out air-gap and act-nate the switch.

Since the linx in the main and by-pass branches of the return magnetic circuit'ot these switches is in the same direction substantially the sum ot the flux in both is acting at the pulling-in air-gap and at all times exerts a force tending to close the switch, being prevented from doing so only when opposed by a greater force at the holding-out air-gap in the by-pass. Consequently, the magnetfis not positive in its operation. The pulling-in force is always greater the higher the current, and, therefore, although it will be overcome and the switch will be held open with extreme heavy currents, as the current drops and nears its predetermined critical or pulling-in'value the switch is liable to close too soon. This is especially true when an alternating current is used to excite the magnet; so much so, that it has never been found possible to use this type of switch commercially for the control of alternating current circuits.

The object of my present invention `is to provide a current-limit magnet which is positive in'its action and is equally reliable both with alternating and direct current excitation.

l have discovered that by the use on a suiably constructed and adjusted magnet frame of two or more coils, a main coil and one er two subsidiary or compensating-coils, suitably wound and placed, l can produce n agnetic fluxes in Opposite directions across one air-cap and all in one direction across theother vair-gap, which fluxes are so responsive to changes in the value of the exciting current, alternating or direct alike, as to give a predominating closingv torce at the pulling-in air-gap whenever the current is below'a predetermined critical value and with currents above such critical value, the force at the pulling-in air-gap remaining substantially stationary or even decreasing while the opposing force rapidly increases with an increase oi current. an increasingly predominating holding-out torce at the holdin `out air-gap. I have thus obtained a gnet which is'positive in its action and l which operates in substantiallythe same way Visentirely reliable with both.

' .In its preferred'form, my improved magnet comprises', briefly stated, a substantially j l varying exciting currents whether alternat- -ing r direct; Fig. 3, a diagram illustrating with alternatino" as with direct currents and E-shaped stationary core having three horizontally projecting legs, an armature oi slightly 'elbow shape'which is pivoted cen-V VV trally on theV outer end of the middle leg of the core to rock at one end against the upper leg or pole-piece and at the other end against the lowerV leg or pole-,piece oi' the core, Y a

" Y main coil which is mountediipon the middle leg ofthe core, .and either Ya single compensating coil connected'in series'rwith the main .coil and woundsirnilarly, which is mounted upon theupper pole-piece, or, the

.equivalent of ysuch Varsingle coil, two coils which are connectedin' series with the main coil andwitli eachother and are mounted Y, one upon the upper and the other upon :the

lower Vpolepiece, the lupper coil beingwound in the same direction as-the main coil andA the lower coil oppositely toboth. .Both the core and the armature are, vof course, laminated in the vusual manner when the magnet is Vintended .ior use withalternating currents.,V rlhe middle leg of -the core is made of smaller cross-section than the other -two legs, preferably of one-'half `the area'of each, in order that this vleg may become easily saturated bythe iiuX created by the main coil .mounted thereon Vand so. prevent the tlux motors, arel shown in the created by the compensating coil or coils Afrom'readilyflowing-through this shorter or shunt path and forcing it Vfrom the upper to thezlower pole-piece and across Vboth airgaps. Where a single compensating coils used, on the upper leg or pulling-n pole of the core, the ampere turns of the main Vand of this'conipensating coil are preferably in the proportion 'of live for the .former to one and v when two compensating given Vto thejsingle coil is divided between the two; And, inally, the armature-isA so shaped` and adjusted that, when the magnet is inoperative and Vin normal open position, there will be a relatively shortpulling-in'airgap atY theupper Vpole-piece and a somewhat longer holding-out air-gap at the bottom polepiece. The proportions and adjustments of the several parts may beV varied widely, but those above given are the ones which, at present,have` been .found to produce the best results. v

The construction'and performance or a switch operated by a. magnet Vhaving the characteristics described, Vand also certain applications or the switch to`control systems both for direct and Vforalternating current drawings,in which-,- Y ,i

li`igure i is aview ofi the switch in side elevation, the -inainrcoil and single commagnet.

V afrzcompanying` paths `indicated by -dotted lines; Fig.=2, a fdiagram showing YVthe characteristic flux and pull curves of the switch of Fig. l under the application of the switch toa direct or singley phasealternating current system of motor control; Fig. 4l, a diagram illustrating a different application of the switch vto a Vdirect or single phase YValternating current system of lmotor control; and Fig. 5, a dia:

grain illustrating one Y application of the switch to a polyphasealternating current system ofV motor control. o

The Vsaine reference characters like VVparts Vthroughout Ythe several figures of the drawings.

Referring iirst to ig. l, Sindica-tes the'k switch as a whole.' rlhe stationary magnetic core l, having three horizontal legs 2,

indicate 3,..andj 4, is lmounted upon Vthe usual base of insulating material '(not shown) or in any other suitable; manner, and above] it is mounted the Vstationary contact member whiclnas shown, is secured to an insulating block 6 rredto the 4topjoi' the upper Vleg ci" the core andris providedV witha binding post 7 by which it is connected with oneV terminalV of' the velectric circuit whichrthe switch 'is used to control. The armature 8,

wliichrcarries at itsupperend the coper-V ating inovable Contact '9 provided with Va suitable binding screw l0 lfor connecting it to the other circuit terminal,is pivoted at il Ybetweentwo platesV l2 (only oney ci' which is shown) iixedto the'oppositesides the middle-'leg of the core. As here illustrated, the VVswitch is moved to and; normally held in open position by a springl which draws the lower end of vthe armature oi the short pulling-inair-gap 15 at the'upper, and the minimum length of the longer ico holding-out air-gap llat the bottom, of the Y' Ywound upon the middle leg 3 of the core,

produces when energized an upward flux 91 across the pullinglin air-gap l5 and a downward viliiX o? across'the holding-out fair-gap j and vhas .ampere turns-three hundred, for eXample-suilicient to easilyV saturate the middle leg orP the core with comparatively small currents. The compensatingcoil 18, preferably of one-fifth the ampere turns of Vthe main coil, is wound upon the upper polepiece of the magnet so as Yto give a flux cpV across the upper or pulling-in*air-gapV in This stop'is preferably so adjusted iso the opposite direction oi' the flux 91, and this flux, beca-use of the saturation of the middle leg by the main coil, is :for the most part forced down to the lower end of the magnet, across the holding-out air-gap in the same direction as the flux 92, and thence back to the upper end of themagnet.

Thus, the closing pull at the upper air" gap is produced by the resultant of the two opposite fluxes 91 and 91, that is -to say, 91 93, wiile the holding-out pull at the lower air gap is produced by the sum of the cooperating fluxes 92 and 93, or 924-93. AWith currents in excess of the predetermined critical value, as appears from the characteristic curves (Fig. 2) given by both alternating and direct currents alike, 'the values of both tluxes 92 and 93 rise, because orp the low iluX densities due tothe length or the lower air-gap, and give a resultant flux, and consequent holding-out pull, which increases rapidly with an increase of current; whereas, the closing pull at the upper air-gap, unlike that of the old series magnets in which the pulling-in airgap is always made longer than the holding-out airgap, remains practicallyfstationary or even decreases in value, since the flux 91 does not rise materially and is opposed by the rising value of the flux 93. Hence, the higher the current, the more strongly is the switch Vheld open and inoperative. As thecurrent in the coils falls to and passes below the critical value, however, the. situation changes. For and instant only the closing and holding-out pulls balance each other. Then, as the flux 91 dies down less rapidly than the opposing flux 93, the gradually weakening closing pull at the upper air-gap quickly rises in value above the lmore rapidly weakening fluxes and holding-out pull at the lower airgap and closes the switch. The kresult is that the switch is positively and vfirmly v,closed whenever the current, whether alternatin-ff or direct, falls slightly below the value predetermined, but is positively pre- .vented from operating by a current slightly in excess of such value and is more'securely locked in inoperative position the heavier and more dangerous the current.

ln F ig. 3, there is villustrated a system oit control for either a direct or single phase alternating current motor in which three of my new electromagnetic switches S, S1, S2 are used as contactors to directly control as many sections of starting resistance R, R1. R2 in the armature circuit ot the motor M. rl"he operation of the Vcontroller in the starting of the motor is as follows: On closing the line switch L, cur-` rent flows from the positive main overwire 30 to and through the motor and thence back to the negative main through all of the resista-nce and both coils ot thel switch S.Y

The switch is held open so long as the current thus admitted to the motor is above the* predetermined safe value, but, as the motor speeds up and-generates counter-electromotive force, the current is reduced in volume andthe switch is closed. Thereupon current flows from the motor back to the negative main through the resistance R2 and B1, over wire 33, through the main coil only and across the closed contacts of switch S, over wire 34, through both coils of switch S1, and over wire 35, short-circuiting the resistance R and the compensating coil of switch S. The switch S1, which in turn is held inoperative until the increased current admitted to the motor by the cutting out of the resistance hasy again been reduced by a further acceleration of the motor, on closing establishes a return circuity Afrom the motor to the negative main which includes the resistance R2, wire 36, closed contacts oi' switch S1, wire 37, both coils of switch S2, wire 38, main coil of switch S1, and wire 35, thereby short-circuiting resistance R1 and the compensating coil ot switch S1 and the main coil of switchV S. Finally, switch S2 closes, after being held open until the motor has sufficiently accelerated, and short-circuits the last section of resistance R2 and .its own compensating coil by establishing a return circuit from the motor by wire 39, closed conta-cts and main coil of switch S2, wire 38, main coil of switch S1, and wire e5 to the negative main.

As illustrated in Fig. 4, the switches are used as relays to control contacter switches which in turn short-circuit the sectionsV of starting resistance. The successive circuits automatically established in the operation of the device, on the closing of the line switch L, are as follows: The lirst circuit includes wire 40, armature of motor M, resistances R2, R1, R, ywire, 4l, both coils of switch S, and wire 42. This starts the motor with the three sections of resistance and both coils of relay S in series with its arma-ture. Then relay S, thus energized, becomes operative it vcloses a shunt circuit, from the positive to the negative main, by wire 43, magnet coil of contactor C, closed contacts of relay S, wire 44, normally closed lower contacts of contactor C2, and wire 45, which actuates the contacter C. The closing of the upper contacts of this contacter short-circuits the resistance R- and both coils of relay S by connecting resistance R1 with the negative main by wire 46, both coils of relay S1, and wire 47, while its lower contacts establish a new or holding circuit for its coil by connecting the lower end of Vthe coil to wire 44 over wire 48. Relay S1, being now energized, closes when conditions permit and places the magnet coil of contactor C1 in the shunt circuit in parallel with the coil of contacter C by connecting wire 43 to Wire 44 over Wires 49and`50. Contacter C1 is. thereupon actuated, its upper contacts Short-circuiting.resistance R1 and both coils of relay'Sl. over Wire 5l, through both coils of relay S2,.and over Wire 52 to Wire 47 and its lower'contacts establishing a .neur holding circuitl for its coil by connecting the lower end of the coil to Wire` 44 over wire 53. The closing of relay S2, in turn,

by connecting-'Wire 49 to Wire 45 .over wiresY 54 vand`r55 and thereby placing the magnet coil ofcontactor C2 in `parallel With the coils Vof thetwo.otherfcontactors, causes the actuation of thisthird contacter, which, vat its up-v per contacts,.short-circuits the three resist- Y ances andboth coils of the three relays vover Wires 56 and 57 and at its lower contacts opens the connection 4between Wires .44 and ,fand thereby :breaks the circuits through the coils ofcontactors -C and C1 and establishesa holding circuit for itself by connecting :the lower end of the coil to Wire-45 over' Wire 5S. The motorA has now been brougl'it to acondition of lfull speechwith all ofthe resistance, the coils of ythe two ,contactors C iand C1, and both coils of the ythree reand,-at its lower contacts. opens the connecV lays cutiout of'circuit.

' The switches :are also used as relays in the controller illustrated in Fig, 5, for alternat'i ing currents only. .Theclosing of the line switch. L connects the -threemahis to the three -Wires 60,61, 62 of the primaryof ythe motor M, which starts the inotor with resistances 'R and 'R1` in each of the'three Wires'64, 65, 66 of its secondary Vor rotor circuitand with both coils of the relay S in series inthe Wirew66. When the relay S, thus energized, is permitted to close, it establishes ay circuit,fshunting two of the primary wires 62 and 61.,.Which includes wire 67, coilofcontactor C, Wire l68, closed con-.

tacts of relay S, Wires 69 and 70, the normally closed contacts on the lower side of the lower contact bar of contactor C1, and

Wires 7l and 72. The contactor C is now 'actuated and its main contacts, in closing, conneet together the threev Wires of Vthe secondary circuitgover the Wiresv 73,74, and 7 5, thusl short-circuiting the resistanceR and bothrrcoils ofthe relay- Sv and'conne'cting both coils of the'V relay S1 inseries with the Wire66, While its lowerA contacts establish a new holding circuit by connecting Wire 6S-to Y Wire 70 over W1re76. vFinally, the relay S1.

is actuated and places the -coil of contactor C1 in parallel with that of contactor C by connecting Wire 67 to'Wire 72 over wires '77, 78,-and 71 and thereby causes the actuation oflcontactor (al, which, at its upper. contacts,.- short-.circuits lresistance R1 and both coilsV of yrelay by connecting togetherrthe Wires Y of the'secondary circuit over Wires 79, 80,81

tion between Wiresv() and 71, thereby cutthe coil of contactor C o'utof circuit,

VAbrLet-teis Eil-tent sand establishes a new .holding circuit for itself by 'connecting VWire 77 directly to Wire 72. Thislcompletes thel operation .of starting the motor.

While TI have shown and Adescribed my ,in-V

llhat l claim las new, Vand-desire 'to secure vl. lnpa motor control'system, the combination, ywith a motor having a plurality of resistancesqfin its circuit,of fa' plurality of contactors controllingeach Va resistance, a plurality of ciirrent-limitV relays controlling each -a contactor, and actuating circuit connections for the relays-and contacter-s Whereby *theiirst relay is actuated by'- current to tlie motor through all of the resistances, the

' actuationfof each Vcontacter to cut out .a Aiesistance beth cuts'out of circuit the relay `by which it iscontrolled land establishes `a new eme onv January 2, 1918, Y

holdin@- circuit Yfor itself and exce at inthe Y s i l case ofthe last contactor, alsoconnectsfthe actuating circuit-'of fthe relay controlling the next succeeding` contacter With lthe motor circuit iii Aseries with theresistaneesl then remaining therein and the last contactor cuts out the holding circuits contactors. Y Y

.2.l In a motor control system, the combination with ainotorfhaving a plurality of of the ypreceding resistances VinA its circuit, of Ya plurality of contactors each having a setof main con'- tacts `and aset of-auxiliary contacts both normally biased V*to open Vposition andthe last'contactor only of the series having anV additional set of auxiliary contacts normally y biased to closed position, za plurality of current-limit relays, and circuit connections forA the lrelays Vand contactors whereby the firstv iio and each succeeding' relay in turn is actu- Y' ated vby kmotor current and on actuation closes the.- actuating circuit of a contactor which, except in-thefcase lof the last contactor, includes therein the normally closedY auxiliary contacts ofthe last lcontactorand eachcontactor on actuatioiliby the closing of itsvmain Vcontacts short-circuits-both arresistance in the mot'or'circuit and l,the actuating circuitY of the relay nby which it is controlled and, except injthe case of the, last coiitactor, also connects the actuating cir-` cuit ofthe relay controllingV the next' succeedingcontactorwith the motor circuit and by the closing-of its normallyopen auxiliary contacts establishes a holding,` circuit for itself and, in the case of the last contactor, by the opening of its normally closed auX- iliary contacts opens the holding circuits of the preceding contactors.

8. In a control system for polyphase induction motors, the combination, with the motor and resistances in the secondary or rotor circuit, of a plurality of contactors controlling each a resistance in the Wires of the secondary circuit, a plurality of current-limit relays, and circuit connections `for the relays and contactors whereby the relays each except the first under control of a contactor are actuated by current in the secondary circuit and the contactors each under control or" a relay are actuated by current outside of the secondary circuit and on actuation each contactor short-circuits the actuating circuit of its controlling relay and establishes a holding circuit for itself and the last contactor opens the holding circuits of all the preceding contactors.

LOUIS LARSEN. 

